I love villains.
Heroes are great, and through them a story is told, but a villain is more important. Yes, your protagonist has to be likable. They have to be relatable. You need to be able to answer the major question, "Why is this story happening to this character at this time?"
But without a compelling villain, nothing else matters.
Luke Skywalker is a whiny farm boy. When Darth Vader and the omnipotent Empire come calling, he becomes a hero.
John McLane is a dopey cop with a failing marriage. When Hans Gruber takes over his wife's office building, he becomes a hero.
Harry Potter is a straight up brat. When Voldemort threatens the entire world, he becomes a hero.
Aloy and Hades? Same thing. Heloise and the Order? Of course. Basically all heroes for all time? You bet your sweet cheeks.
Villains make the hero, and I love making villains.
Writing a story is all about balance. In fact, all stories are about balance. You have the status quo at the beginning, a major shakeup, and the rest of the story is about finding balance in the "new normal."
In the same way, your characters act as weights on either end of the scale. Your hero must be suitably heroic, but they must also be balanced out by the evil on the other side.
Actually, "Evil" is a loaded word. Let's put it this way: Both sides need to see themselves as the hero.
You've probably heard that one before. "No villain thinks themselves the villain." It's true because, well, that's how it is in life. No one is waking up in the morning thinking "Man, I cannot WAIT to get some evil done today." Everyone thinks they are the hero of the story. Just as every side character thinks they are the lead. Every background extra has their own stuff going on.
If you write your villains as two-dimensional cartoons, you're not just doing them a disservice. You're undercutting your hero.
Even the most "capital E Evil" stuff in human history was done by people in the name of the "greater good." Do you think the Nazis were ashamed of what they did? Or that John Wilks Booth knew he'd be a villain for all of history? Do you think slave owners lamented how this was all wrong, but damn they need help picking cotton?
No. Evil people always think they are heroes of their own narrative. Some people even acknowledge that the steps they are taking are dire, but they convince themselves (and many others) that the stakes are too high to do otherwise. In fact, a true villain is disgustingly normal and charming. You'd like them, if you didn't know them.
A villain should be someone you're drawn to. Instead of writing them as the person you hate the most, pick someone you admire. Then twist a few of their traits to the extreme. Extremism of any form can lead to vile villainy.
Try to write the story from their perspective (Note: Don't actually write the whole story from their perspective. That's a lot of work). How would you view it--and cause the audience to view it--so that they come out the hero?
Luke Skywalker murders hundreds of thousands of people aboard the Death Star, but he is the hero. Nathan Drake kills, conservatively, a million henchmen, and he jokes about it the whole time. Lara Croft is a kleptomaniac with psychopathic tendencies, and she's a tent-pole franchise.
For this week, try this exercise. Take a villain you love to hate. One you know intimately. Now, just for fun, write them as the hero. What excuses can you make for their wanton murder? Their malevolence? Their ambitions?
For a GREAT take on villains, I recommend Myke Cole's "The Armored Saint." I literally could not put it down. And it is a great example of a villain whom, from not even that different a point of view, is the hero.